N,N-dimethyl imidodicarbonimidic diamide acetate, method for producing the same and pharmaceutical compositions comprising the same

ABSTRACT

The present invention relates to N,N-dimethyl imidodicarbonimidic diamide acetate, a method of preparing the same and a pharmaceutical composition comprising the same, and more particularly, to N,N-dimethyl imidodicarbonimidic diamide acetate which is a crystalline acid addition salt prepared by reacting N,N-dimethyl imidodicarbonimidic diamide with acetic acid, and which is very effective as a therapeutic agent for treating metabolic syndromes that glycosuria and diabetes mellitus, obesity, hyperlipidemia, fatty liver, coronary heart disease, osteoporosis, polycystic ovarian syndrome, a cancer depleted of gene P53, etc. are complexly occurred; treating diabetes mellitus and preventing its complication; and treating a cancer and preventing myalgia, muscle cell cytotoxicity and rhabdomyolysis, etc. since the acid addition salt is excellent in physicochemical properties such as solubility, stability, non-hygroscopicity, anti-adhering property, etc., and low toxicity, a method of preparing the same and a pharmaceutical composition comprising the same.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 12/524,695, filed Jul. 27, 2009, presently allowed,which is a 35 U.S.C. §371 National Phase filing of InternationalApplication No. PCT/KR2008/000529, filed Jan. 29, 2008, which claimspriority to Korean Application No. 10-2007-0008835, filed Jan. 29, 2007.The entire content of each prior application is hereby incorporated byreference.

TECHNICAL FIELD

The present invention relates to N,N-dimethyl imidodicarbonimidicdiamide acetate, a method of preparing the same and a pharmaceuticalcomposition comprising the same, and more particularly, to N,N-dimethylimidodicarbonimidic diamide acetate which is a crystalline acid additionsalt prepared by reacting N,N-dimethyl imidodicarbonimidic diamide withacetic acid, and which is very effective as a therapeutic agent fortreating metabolic syndromes that glycosuria and diabetes mellitus,obesity, hyperlipidemia, fatty liver, coronary heart disease,osteoporosis, polycystic ovarian syndrome, a cancer depleted of geneP53, etc. are complexly occurred; treating diabetes mellitus andpreventing its complication; and treating a cancer and preventingmyalgia, muscle cell cytotoxicity and rhabdomyolysis, etc. since theacid addition salt is excellent in physicochemical properties such assolubility, stability, non-hygroscopicity, anti-adhering property, etc.,and low toxicity, a method of preparing the same and a pharmaceuticalcomposition comprising the same.

More particularly, the present invention relates to novel N,N-dimethylimidodicarbonimidic diamide acetate that lowers dissolution rate andimproves the permeability to enhance its bioavailability in a lowergastrointestinal tract.

BACKGROUND ART

N,N-dimethyl imidodicarbonimidic diamide has general name of metformin,and is a therapeutic agent for Non-Insulin Dependent Diabetes Mellitus,and a biguanide based pharmaceutical that is most excellent inhypoglycemic action and preventing the complication.

It was suggested in various articles that only metformin has a propertyas the first choice as oral anti-diabetic agent. In particular, theclinical effect of the metformin was proved by its pharmacologicalaction as AMPK activator. It was reported that AMPK is a key enzymecontrolling the metabolism of carbohydrate and lipid physiologically;metformin activates this enzyme, thereby normalizing high blood-glucoselevel, improving lipid state, normalizing menstrual irregularity, inovulation, and treating a fatty liver; and metformin is effective intreating or preventing a cancer depleted of gene P53.

Abramson Cancer Center of Medical college, Pennsylvania reported througha professional journal for cancer that metformin is effective as AMPKactivator in treating or preventing a cancer depleted of gene P53[Monica Buzzai, et al. Systemic Treatment with the Antidiabetic DrugMetformin Selectively Impairs p53-Deficient Tumor Cell Growth, CancerRes 2007; 67:(14). Jul. 15, 2007].

In other words, if a human body is subjected to an unfavorablecondition, metformin activates AMPK enzyme, which controls an energymetabolism applied to the condition, thereby controlling glucose andlipid, and removing cancer cells.

Gene P53 renders a damaged cell or an unnecessary cell and an aged cellto kill itself (apoptosis). If a cancer cell is mutated, the gene P53 isdepleted, thereby forming incurable cancer cell.

It was verified from experiments that metformin activates the AMPKenzyme of an incurable cancer cell depleted of the gene P53, therebychanging the metabolic path, and accordingly, the cancer cell is killedsince it could not adapt itself to the changed metabolic path.

The report suggests that gene P53 removes a cancer and maintainslongevity by employing an energy metabolism control enzyme named asAMPK.

Metformin is a drug that activates the AMPK thereby normalizing glucoseand lipid metabolism. It was found that if metformin is administered toa cancer depleted of the gene P53, the energy metabolic path for thecancer cell is changed, and anticancer action increases proportionallyto a dosage of metformin, and further metformin is effective in treatinga cancer in a normal dosage for treating diabetes mellitus.

Further, researchers of the medical center of Beth Israel Deaconess,Boston, United States reported through a professional medical journalthat metformin is effective as PGC-1α activator in preventing severeside effects such as myalgia, muscle cell damage and rhabdomyolysis[Jun-ichi Hanai, et al. The muscle-specific ubiquitin ligaseatrogin-1/MAFbx mediates statin-induced muscle toxicity, J. Clin.Invest. 117: 3940-3951 (2007)].

Expression of Atrogin-1 gene causes muscle toxicity such as myalgia,muscle cell damage and rhabdomyolysis, but metformin inhibits theexpression of Atrogin-1 gene due to PGC-1α transcription factoractivity, thereby inhibiting and preventing muscle disorder due to theincrease of the expression of Atrogin-1 gene.

Metformin is administered in the form of pharmaceutically acceptableacid addition salt since metformin is pharmaceutically useful in theform of a free base, but the stability of the form is low.

Korean Patent No. 90,479 describes that four physicochemical standardssuch as (1) excellent solubility; (2) excellent stability; (3)non-hygroscopicity; and (4) the processibility as a tablet form must besatisfied for preparing in the form of pharmaceutically acceptable salt.It is very difficult to satisfy the four standards as a pharmaceuticallyacceptable acid addition salt.

Research for addition salt other than metformin hydrochloride has beenperformed. U.S. Pat. No. 3,957,853 discloses metformin acetyl salicylicacid salt, U.S. Pat. No. 4,028,402 discloses a novel addition salt ofbiguanide compound, and U.S. Pat. No. 4,080,472 discloses thepreparation of metformin chlorfibric acid salt and treatment of diabetesmellitus related diseases. Further, U.S. Pat. No. 6,031,004 describes amedical composition by fumarate, succinate and maleinic acid ofmetformin, and its use. Although the research for metformin additionsalt has been continuously performed, metformin is approved in only adrug as hydrochloride, and is widely prescribed as a therapeutic agentfor non-insulin dependent diabetes mellitus. Metformin hydrochloride isthe material that is almost exclusively absorbed in upper smallintestine. Accordingly, it is incompletely absorbed in lower smallintestine, and thus it is a salt very difficult to formulate as acontrolled release drug for 24 hours. This is why the solubility ofmetformin hydrochloride is high (Marathe, P. et al., Br. J. Clin.Pharmacol., 50:325-332 (2000)).

Research for addition salt other than metformin hydrochloride has beenperformed. U.S. Pat. No. 3,957,853 discloses metformin acetyl salicylicacid salt, U.S. Pat. No. 4,028,402 discloses a novel addition salt ofbiguanide compound, and U.S. Pat. No. 4,080,472 discloses thepreparation of metformin chlorfibric acid salt and treatment of diabetesmellitus related diseases. Further, U.S. Pat. No. 6,031,004 describes amedical composition by fumarate, succinate and maleinic acid ofmetformin, and its use. However, the preparation method and compositionof metformin acetate had not been mentioned in the prior patents.Further, there is no known or progressed research for the effect ofmetformin acetate.

Although the research for metformin addition salt has been continuouslyperformed, only metformin hydrochloride is actually used. Hydrochloridesalt is large in its unit dosage and its formulation size is very large.Accordingly, even though a novel addition salt is attempted, itsmolecular weight and formulation becomes too large, and thus it isinferred that it is difficult to formulate. Accordingly, it isconsidered that the development of a product for a novel addition salthad not been attempted.

Meanwhile, prior patent (U.S. Pat. No. 4,080,472) describes that whenmetformin free base is prepared, an ion exchange resin column is usedfor removing hydrochloric acid from metformin hydrochloride, and priorpatent describes that severe preparation condition that a solvent isrefluxed with heating and filtered in hot state is required.

The usual dosage of metformin hydrochloride is 2550 mg at maximum daily,i.e., 500 mg or 750 mg tablet is administered 2˜3 times with a diet aday.

Such an administration method causes drastic changes in the drug levelin blood due to the properties of metformin hydrochloride having quickdrug elimination rate, and such a change in drug level in blood canresult in side effects and resistance to the drug. Actually, the sideeffects related to the use of metformin hydrochloride occur frequentlyin gastrointestinal tract, and the examples include anorexia, nausea,vomiting and occasionally diarrhea. Accordingly, a research for extendedcontrolled release formulation of metformin hydrochloride is beingprogressed in order to decrease such side effects and improve thetreating quality of the Type 2 diabetic patients.

Further, metformin hydrochloride is highly water soluble drug (>300mg/mL, 25□), and thus if it is not designed as special formulation,excessive drop in blood glucose by drastic release phenome can becaused. Accordingly, it is considered that a controlled release tabletdesigned so that defined dose of the drug can be control-released for 24hours is preferable administration form in the aspect of a patient'sconvenience as well as therapeutic effect.

However, metformin hydrochloride is highly soluble in water, and hardlypermeates the lower gastrointestinal tract, and thus the most drug mustbe absorbed at upper gastrointestinal tract. Therefore, there are manyproblems in preparation technology for preparing special formulation forcontrolled release.

Many patents for controlled release tablet of metformin for overcomingsuch problems in the pharmaceutical technology are registered at homeand abroad. Korean Patent Application No. 1999-7011439 filed in the nameof Depomed Inc. describes a controlled release formulation that releasesa drug for 8 hours using general high molecular polymer as a formulationfor controlled release of a soluble drug. Korean Patent Application No.2000-7010280 filed in the name of Bristol Meyer's Squibb describes 2phase controlled release tablet suitable for controlled release ofmetformin having high solubility in a desired degree.

However, since the unit dosage of metformin is large, i.e., 500 to 750mg, the total weight of the tablet is very heavy in consideration ofadding a pharmaceutical excipient including a controlled release agent.Further, since the solubility of metformin hydrochloride is high, thecontrolled release agent to be added is also needed in much amount inorder to controlled-release for desired time, and accordingly theformulation may be too large to take easily. Accordingly, it is not easyto maintain continuous controlled release of metformin hydrochloridewithin the size that a patient can take the tablet.

The reason why metformin acetate is selected as an anti-diabetic agentis that it can cause pharmaceutically excellent controlled release andthe pharmacological effect of metformin acetate is superior to that ofmetformin hydrochloride.

Recently, researches for various pharmacological effects of acetate areactively progressed. Many experiments that small amount of vinegarlowers blood glucose at 30 minutes after meal by inhibiting an enzyme todegrade disaccharide to glucose in intestine have been reported.

Recently, research by Carol Johnston et al for the effect of vinegarperformed for patients having type 2 diabetes mellitus mentioned that64% of blood glucose after meal is decreased and 34% of insulinsensitivity is also decreased in vinegar administration group amonginsulin resistant group [Vinegar: Medicinal uses and Antiglycemic effectCarol Johnston, et al. Medscape general medicine 2006; 8(2):61].

Further, Ogawa mentioned that acetic acid inhibits the activity ofdisaccharidase such as sucrase and lactase. In other words, he mentionedthat acetic acid plays a role in decreasing blood glucose by inhibitingthe action of an enzyme degrading polysaccharide to monosaccharide.

References

1. Ogawa N, Satsu H, Watanabe H, et al. Acetic acid suppresses theincrease in disaccharidase activity that occurs during culture of caco-2cells. J. Nutr. 2000 March; 130(3):507-13

2. Carol S. Johnston, PhD, R D; Cindy A. Gaas, B S. Vinegar: MedicinalUses and Antiglycemic Effect, Medscape General Medicine. 2006; 8(2):61.

3. Ostman E, Granfeldt Y, Persson L, Björck I. Vinegar supplementationlowers glucose and insulin responses and increases satiety after a breadmeal in healthy subjects. Eur J Clin Nutr. 2005 September; 59(9), 983-8.

4. Johnston C S, Kim C M, Buller A J. Vinegar improves insulinsensitivity to a high carbohydrate meal in subjects with insulinresistance or type 2 diabetes. Diabetes Care. 2004 January; 27(1):281-2.

5. Leeman M, Ostman E, Bjorck I. Vinegar dressing and cold storage ofpotatoes lowers postprandial glycaemic and insulinaemic responses inhealthy subjects. Eur J Clin Nutr. 2005 November; 59(11):1266-71.

6. Ebihara K, Nakajima A. Effect of acetic acid and vinegar on bloodglucose and insulin responses to orally administered sucrose and starch.Agric Biol. Chem. 1988; 52:1311-1312.

7. Brighenti F, Castellani G, Benini L, et al. Effect of neutralized andnative vinegar on blood glucose and acetate responses to a mixed meal inhealthy subjects. Eur J Clin Nutr. 1995 April; 49(4):242-7.

Korean Patent Application No. 2004-7013025 filed by Mitsukan Company,Japan describes a food and medical composition for preventinghypertension characterized in that minute amount of acetic acid showsexcellent action of lowering blood pressure by oral intake for a longperiod.

Researches for vinegar and acetic acid itself on various diseases havebeen actively performed. However, the research shows considerableeffects as outcome of the research for vinegar as food not experimentfor acetate, it did not show the effect as metformin acetate as shown inthe present invention, and it did not mentioned the effect forinteraction with metformin.

The present inventors decided that departing from the paradigm that theproblem of metformin hydrochloride must be overcome by designing aformulation through selecting a proper controlled release agent, if thesolubility of the active ingredient is lowered, side effects such asexcessive drop of blood glucose level or a disorder in gastrointestinaltract is improved even on taking immediately release tablet, and moreefficient controlled release can be performed on formulating theimmediately release preparation; and studied on metformin addition salthaving relatively low solubility to water. However, there is a problemin practicability since if the molecular weight of a novel metforminderivative is very high compared to metformin hydrochloride even thougha metformin derivative having low solubility is synthesized, the dosageof metformin is increased. This is a crucial problem on considering theunit dosage of metformin is large. If a metformin addition salt, whichhas not too large molecular weight thereby having dosage capable ofbeing compressed as a tablet, is easy to be control-released due tolowered solubility, and has relatively excellent permeability at lowergastrointestinal tract and colon, and thus has relatively wideabsorption site compared to metformin hydrochloride, is developed, itwill have excellent ripple effect pharmaceutically orpharmaco-dynamically.

DISCLOSURE OF INVENTION Technical Problem

The present inventors decided that departing from the paradigm that theproblem of metformin hydrochloride must be overcome by designing aformulation through selecting a proper controlled release agent, if thesolubility of the active ingredient is lowered, side effects such asexcessive drop of blood glucose level or a disorder in gastrointestinaltract is improved even on taking immediately release tablet, and thecontrol of drug release can be performed more efficiently; and studiedon metformin addition salt having relatively low solubility to water.However, if the molecular weight of a novel metformin derivatives isvery high compared to metformin hydrochloride, there is a problem inpracticability even though a metformin derivative having low solubilityis synthesized, because of the increased dosage of metformin. This is acrucial problem on considering the unit dosage of metformin is large. Ifa metformin addition salt, which has not too large molecular weightthereby having dosage capable of being compressed as a tablet, is easyto control the drug release rate due to lowered solubility, and hasrelatively excellent permeability at lower gastrointestinal tract andcolon, and thus has relatively wide absorption site compared tometformin hydrochloride, is developed, it will have excellent rippleeffect pharmaceutically or pharmaco-dynamically.

If the pharmacological effect of the addition salt can show the synergiceffect with the active pharmacological ingredient of metformin, it willbe more idealistic metformin addition salt. From the result of acontinuous research, the present inventors completed the presentinvention by discovering metformin acetate having not too largemolecular weight and having relatively low solubility.

Further, the present inventors performed various clinical researches formetformin acetate, and discovered that the metformin acetate haspharmaceutical and pharamacokinetic advantage attainable due to lowsolubility, and is relatively more excellent compared to metforminhydrochloride in the effects of initial drop in blood glucose and dropin blood glucose after meal. This suggests that even though the unitdosage of metformin acetate less than that of metformin hydrochloride isadministered, the same clinical effect as metformin hydrochloride can beobtained, and accordingly its excellent ripple effect can be alsoexpected pharmacologically.

Therefore, the object of the present invention is to providepharmaceutically acceptable metformin acetate having excellentphysicochemical properties such as solubility and stability, and amethod of preparing the same.

Further, another object of the present invention is to provide apharmaceutical composition for treating or preventing diabetes mellitusand its complication comprising metformin acetate as an activeingredient.

Still another object of the present invention is to provide apharmaceutical composition for treating or preventing diabetes mellitusand its complication comprising metformin acetate having relatively lowsolubility in water as an active ingredient.

Still another object of the present invention is to provide a method ofpreparing metformin acetate.

Still another object of the present invention is to provide animmediately release or controlled release metformin formulationcomprising metformin acetate as an active ingredient, which controlsexcellent drug release even using less controlled release agent comparedto metformin hydrochloride, and has more clinically excellent effects ofinitial drop in blood glucose and drop in blood glucose after meal thanthat of metformin hydrochloride.

Further, the absorption speed of metformin in gastrointestinal tract canbe controlled by extending the gastric retention time of a drug throughusing metformin as an active ingredient and a matrix agent capable ofcontrolling the release rate of the metformin. Therefore, the size of atablet can be designed in a small level suitable to take since therelease of the drug is continuously and sufficiently achieved for 24hours even when the controlled release matrices according to the presentinvention are formulated in less amounts than that of the matricesrequired in preparing previous controlled release tablet.

Technical Solution

The present inventors completed the present invention by preparingmetformin acetate, a method of preparing the same and a compositioncomprising the same useful as a therapeutic agent for diabetes mellitus

The present invention is comprised of the following twelvecharacteristic features:

(1) metformin acetate represented by formula 1 below;

(2) metformin acetate according to the above (1) in the form ofanhydrous, hemihydrate or monohydrate;

(3) a method of preparing the metformin acetate of formula 1 comprisingreacting 1 equivalent of the metformin hydrochloride of formula 4 belowwith 1 to 2 equivalent of inorganic salts in water or an organic solventto generate metformin free base; and then reacting with 1 to 2equivalent of acetic acid of formula 2 below with or without removingthe inorganic salt;

(4) a method of preparing the metformin acetate of formula 1 comprisingreacting 1 equivalent of the metformin hydrochloride of formula 4 with 1to 2 equivalents of an organic alkali in water, and then reacting withacetic acid of formula 2 without removing inorganic salt;

(5) a method of preparing the metformin acetate of formula 1 comprisingreacting 1 equivalent of the metformin hydrochloride of formula 4 with 1to 2 equivalents of inorganic salts or an organic alkali in water, andthen reacting with 1 to 2 equivalents of acetic acid of formula 2without removing inorganic salt;

(6) the method of preparing the metformin acetate according to the above(3) or (4) comprising reacting 1 equivalent of metformin free base with1 equivalent of acetic acid;

(7) the method of preparing the metformin acetate according to the above(3) wherein the organic solvent is selected from the group consisting ofmethanol, ethanol, isopropanol, acetone and acetonitrile;

(8) the method of preparing the metformin acetate according to the above(3) wherein 1 equivalent of metformin hydrochloride and 1 to 2equivalents of inorganic salts are reacted in water or an organicsolvent to generated metformin free base;

(9) a pharmaceutical composition comprising the metformin acetate of theabove (1) as an active ingredient, for treating diabetes mellitus ofpatients having metabolic syndromes that glycosuria and diabetesmellitus, obesity, hyperlipidemia and coronary heart disease arecomplexly occurred, and preventing its complication;

(10) the pharmaceutical composition according to the above (9) whereinthe composition is formulated in the form of a tablet or a capsule;

(11) the pharmaceutical composition according to the above (10) whereinthe composition further comprises a pharmaceutically acceptable carrier,a diluent or an excipient; and

(12) the pharmaceutical composition according to the above (9), (10) or(11) wherein the composition is effective in preventing and treatingtype 2 diabetes mellitus, controlling body weight, loweringhyperlipidemia lipid, treating fatty liver, preventing coronary heartdisease, treating polycystic ovarian syndrome, treating a cancerdepleted of gene P53, and preventing myalgia, muscle cell cytotoxicityand rhabdomyolysis by orally administering 50 to 3,000 mg of themetformin acetate of formula 1 as a free base a day over 1 to 3 times.

Advantageous Effects

Metformin acetate according to the present invention gives moreexcellent drop effect in blood glucose level than that of metforminhydrochloride used previously as an anti-diabetic agent, and inparticular, gives very excellent drop effect in blood glucose levelbefore meal as well as after meal, and increases insulin sensitivity.More particularly, the metformin acetate gives pharmaceutically andphamacodynamically excellent effect showing effective control of a drugrelease by lowering solubility compared to that of the metforminhydrochloride. Further, the metformin acetate according to the presentinvention is proper in the size of molecular weight, and superior inpharmaceutical, pharmacological or clinical aspects to metforminhydrochloride. The metformin acetate according to the present inventionis slowly released in small intestine on oral intake, and issimultaneously separated to metformin and acetic acid, and thenmetformin is absorbed and acetic acid inhibits the degradation ofdisaccharide in small intestine thereby inhibiting rise in blood glucoselevel. The metformin acetate is a compound pharmaceutically veryexcellent to show optimum bioavailability.

Further, the method of preparing the metformin acetate according to thepresent invention established the steps so that it can be progressedsimply and without special equipment. The method of preparing themetformin acetate according to the present invention can synthesize anovel metformin salt with a low cost by improving the steps simplythereby elevating industrial applicability so that the synthesis can beperformed in general production equipment without special equipment.

The metformin acetate according to the present invention is acrystalline acid addition salt suitable for preparing a pharmaceuticalformulation compared to previous metformin hydrochloride prepared byusing hydrochloric acid, which is a biguanide compound using only onesalt as drug. Further, the metformin acetate is a novel drug thatincreases pharmaceutical and physicochemical advantages such asstability, non-hygroscopicity and processibility as a tabletformulation, as well as increases the therapeutic effect for diabetesmellitus and its complication even though acetic acid having relativelylow toxicity compared to that of the metformin hydrochloride is used.

Table 1 below compares the oral toxicity of hydrochloric acid forming acrystalline acid addition salt of the metformin hydrochloride and aceticacid forming a crystalline acid addition salt of the metformin acetate.The toxicity data for two acids were excerpted from Registry of ToxicEffects of Chemical Substances (RTECS) Data.

TABLE 1 Administration Subject Dose Dose Acid path animal (LD50) (TDLo)Hydrochloric Intraperitoneal Mouse 40 mg/kg — acid Oral Rabbit 900 mg/kg— Acetic acid Intravenous Mouse 525 mg/kg — Oral Rat 3,310 mg/k g — OralHuman — 1,470 μg/kg being LD50: 50% lethal dose, TDLo; lowest toxic dose

As indicated in the Table 1, hydrochloric acid used in preparing acrystalline acid addition salt of the metformin is toxic itself, butacetic acid used in the present invention is very safe compared tohydrochloric acid. From in vivo and in vitro experiments for thepharmacological effect of the metformin acetate performed in severalways, it could be anticipated that the metformin acetate is moreexcellent compared to the metformin hydrochloride in the effect of dropin blood glucose, action of decreasing lipid and improvement inmetabolic syndrome, as well as therapeutic purpose can be achieved evenwith less dosage than the metformin hydrochloride.

DESCRIPTION OF DRAWINGS

FIG. 1 is the result of XRD measurement for metformin acetate of Example1 according to the present invention.

FIG. 2 is the result of XRD measurement for metformin hydrochloride ofComparative example 1.

FIG. 3 is the result of NMR measurement for metformin acetate of Example1 according to the present invention.

FIG. 4 is the result of NMR measurement for metformin hydrochloride ofComparative example 1.

FIG. 5 is the result of IR measurement for metformin acetate of Example1 according to the present invention.

FIG. 6 is the result of IR measurement for metformin hydrochloride ofComparative example 1.

FIG. 7 is the result of solubility measurement for Experimental example2 according to the present invention.

FIG. 8 is the result of hygroscopicity measurement for Experimentalexample 3 according to the present invention.

FIG. 9 is the result of pKa measurement for metformin acetate accordingto the present invention.

FIG. 10 is the result of dissolution measurement for the controlledrelease tablet of metformin acetate of Example 10 according to thepresent invention and the controlled release tablet of metformin acetateprepared by Comparative example 2.

MODE FOR INVENTION

The present invention relates to novel metformin acetate of formula 1below that is more superior in the physicochemical properties such assolubility, stability, non-hygroscopicity and processibility as a tabletformulation, and is more effective in treating or preventing diabetesmellitus and its complication:

Further, the present invention provides a method of preparing metforminacetate of formula 1 comprising adding a base to the metforminhydrochloride of formula 4 in water or an organic solvent to generatemetformin free base represented by formula 3 below; and reacting theresulting metformin free base with acetic acid represented by formula 2below, as described in reaction scheme 1 below:

The preparation method as described in the reaction scheme 1 comprises

1) removing the addition salt of the metformin hydrochloride of formula4;

2) adding acetic acid of formula 2 to a reaction solution of themetformin of formula 3 to prepare a mixture; and

3) stirring the mixture, and filtering, washing and drying the resultingsolid to form a novel crystalline acid addition salt of formula 1.

The crystalline acid addition salt of the metformin according to thepresent invention is prepared by adding acetic acid to a solutioncontaining metformin represented by formula 3 comprising the followingsteps.

In the first step, inorganic salts can be used under water or an organicsolvent condition in order to obtain metformin free base. The examplesof the inorganic salts include alkali hydroxide such as sodium hydroxideand potassium hydroxide, and sodium hydroxide is preferably used. 1 to 2equivalents of the inorganic salts can be used for 1 equivalent ofmetformin hydrochloride.

In the second step adding acetic acid to a reaction solution containingmetformin, 1 to 2 equivalent of acetic acid is preferably used for 1equivalent of metformin hydrochloride.

In the first and the second steps, an usual solvent is used as areaction solvent, and preferably, an organic solvent selected from thegroup consisting of methanol, ethanol, isopropanol, acetone andacetonitrile is used.

The third step is a step of forming a crystalline acid addition salt,and is carried out in a temperature range of −10 to 80° C.

As more simplified process, a method of preparing metformin acetatewithout performing the first and the second steps is provided. Themetformin acetate can be prepared by reacting metformin hydrochloridewith an organic alkali under water or an organic solvent condition, andsodium bicarbonate, potassium carbonate and sodium acetate can used asthe organic alkali used in preparation process, and sodium acetate ispreferably used. Further, as depicted in reaction scheme 2, themetformin acetate can be also prepared by reacting metforminhydrochloride simultaneously with acetic acid and inorganic salt, andalkali hydroxide such as sodium hydroxide and potassium hydroxide can beused as the inorganic salt used in the preparation process, and sodiumhydroxide is preferably used. 1 to 2 equivalents of the organic alkalican be used for 1 equivalent of metformin hydrochloride.

The term metformin acetate herein refers to metformin (1:1) acetateunless mentioned otherwise.

The metformin acetate according to the present invention includes bothanhydrous and hydrate, and preferably anhydrous.

According to the present invention, a process for preparing metforminfree base was established so that the process could be performed simplyand without any special equipment. For removing hydrochloric acid of themetformin hydrochloride, U.S. Pat. No. 4,080,472 uses ion exchange resincolumn, or U.S. Pat. No. 4,028,402 discloses a preparation method thatis carried out under severe conditions of heating to reflux andfiltering hot solution. However, the present invention can prepare anorganic acid salt of metformin with less cost by simplifying the processso that it can be prepared in general production equipment without anyspecial equipment, thereby rising industrial applicability. The methodof preparing this free base can be employed in a reaction with variousacids used in preparing a pharmaceutically acceptable salt.

The kind of the pharmaceutically acceptable salt applicable to themethod of synthesizing a free base according to the present invention isas follows: hydrochloride, sulfate, nitrate, phosphate, sulfite,dithionate, acetate, benzoate, citrate, glycolate, glyoxylate,mercaptoacetate, y-hydroxy butyrate, palmoate, aspartate, glutamate,pyrrolidone carboxylate, methane sulfonate, naphthalene sulfonate,glucose-1-phosphate, chlorophenoxy acetate, embonate, chlorophenoxyacetate, maleate, parachlorophenoxy isobutylate, formate, lactate,succinate, tartrate, cyclohexane carboxylate, hexanoate, octanoate,decanoate, hexadecanoate, octodecanoate, benzene sulfonate,trimethoxybenzoate, paratoluene sulfonate, adamantane carboxylate,glutamate, pyrrolidone carboxylate, malonate, malate, oxalate, etc.

Further, the present invention relates to a pharmaceutical compositionfor treating or preventing diabetes mellitus comprising metforminacetate of the formula 1 as an active ingredient and having variousformulations.

The metformin acetate according to the present invention prepared by theabove method comprises a pharmaceutically acceptable carrier, and thuscan be applied as an oral preparation in various forms, and employed inpreparing a pharmaceutical preparation for treating or preventingdiabetes mellitus related disease state in the form of acontrolled-release and immediately-release tablet, a soft capsule, ahard capsule, a pill, a granule or a powder, an injecting agent and aliquid preparation.

A controlled-release tablet capable of controlling the dissolution rateof a drug among the various oral preparations mentioned above isconsidered as most preferable administration form, in an aspect that itcan prevent drastic change in level in blood and prevent side effectsand resistance to a drug, and in consideration of the convenience andtreating effect of a patient.

An ingredient selected from an enteric polymer, a hydrophobic compound,and a hydrophilic polymer is used as a matrix agent used for controlledrelease among the pharmaceutically acceptable carrier. As the entericpolymer, a mixture of at least one or two compound selected frompolyvinylacetate phthalate, methacrylic acid copolymer,hydroxypropylmethyl cellulose phthalate, shellac, cellulose acetatephthalate, cellulose propionate phthalate, (poly-(methacrylicacid/methyl-methacrylate) copolymer) can be used, andhydroxypropylmethyl cellulose phthalate is preferably used.

The hydrophobic compound can be selected from pharmaceuticallyacceptable polyvinyl acetate, poly-methacrylate copolymer, for example,poly-(ethyl acrylate/methyl methacrylate) copolymer,poly-(ethylacrylate/methyl methacrylate/trimethyl amino ethylmethacrylate) copolymer, ethyl cellulose and cellulose acetate, fattyacid and fatty acid ester, fatty acid alcohol, wax and inorganiccompound, etc. Specifically, at least one or two compounds can beselected from glyceryl palmitostearate, glyceryl stearate, glycerylbehenate, cetyl palmitate, glyceryl monooleate and stearic acid as fattyacids and fatty acid esters; cetostearyl alcohol, cetyl alcohol andstearyl alcohol as fatty acid alcohols; carnauba wax, bees wax andmicrocrystalline wax as waxes; talc, precipitated calcium carbonate,dibasic calcium phosphate, zinc oxide, titanium oxide, kaolin,bentonite, montmorillonite and vee gum as inorganic compounds, etc.

Examples of the hydrophilic polymer include, but are not limited to, asaccharide, a cellulose derivative, a gum, a protein, a polyvinylderivative, a polymethacrylate copolymer, a polyethylene derivative, acarboxyvinyl polymer and a mixture thereof. Specifically, examples ofthe saccharides include, but are not limited to, dextrin, polydextrin,dextran, pectin and pectin derivative, alginate, poly(galacturonicacid), xylan, arabinoxylan, arabinogalactan, starch, hydroxypropylstarch, amylase, amylopectin and a mixture thereof; examples of thecellulose derivatives include, but are not limited to,hydroxypropylmethyl cellulose, hydroxypropyl cellulose, hydroxymethylcellulose, hydroxyethyl cellulose, methyl cellulose, carboxymethylcellulose sodium, hydroxypropyl methyl cellulose acetate succinate,hydroxyethylmethyl cellulose and a mixture thereof; examples of the gumsinclude, but are not limited to, guar gum, locust bean gum, tragacantha,carrageenan, gum acasia, gum arabic, gellan gum, xanthan gum and amixture thereof; examples of the proteins include, but are not limitedto, gelatin, casein, zein and a mixture thereof; examples of thepolyvinyl derivatives include, but are not limited to, polyvinylalcohol, polyvinyl pyrrolidone, polyvinylacetal diethylaminoacetate anda mixture thereof; examples of the polymethacrylate copolymers include,but are not limited to, poly(butyl methacrylate,(2-dimethylaminoethyl)methacrylate, methylmethacrylate) copolymer,poly(methacrylic acid, methylmethacrylate) copolymer, poly(methacrylicacid, ethylacrylate) copolymer and a mixture thereof; examples of thepolyethylene derivatives include, but are not limited to, polyethyleneglycol, polyethylene oxide and a mixture thereof; and examples of thecarboxyvinylpolymers include, but are not limited to, carbomer.

Examples of the pharmaceutically acceptable diluent within a rangedamaging the effect of the present invention include, but are notlimited to, starch, microcrystalline cellulose, lactose, glucose,mannitol, alginate, alkali earth metal salt, clay, polyethylene glycoland dicalcium phosphate, etc. Examples of the binder include, but arenot limited to, starch, microcrystalline cellulose, highly dispersivesilica, mannitol, lactose, polyethylene glycol, polyvinyl pyrrolidone,hydroxypropyl methylcellulose, hydroxypropyl cellulose, natural gum,synthetic gum, copovidone and gelatin, etc. Examples of the disintegrantinclude, but are not limited to, starch or denatured starch, forexample, sodium starch glycolate, corn starch, potato starch orpre-gelatinized starch, etc; clay, for example, bentonite,montmorrilonite and veegum, etc.; cellulose, for example,microcrystalline cellulose, hydroxylpropyl cellulose or carboxymethylcellulose, etc.; algin, for example, sodium alginate or alginic acid;crosslinked cellulose, for example, croscarmellose sodium, etc.; gum,for example, guar gum and xanthan gum, etc.; crosslinked polymer, forexample, crospovidone; effervescent preparation, for example, sodiumbicarbonate and citric acid, etc. Examples of the lubricant include, butare not limited to, talc, magnesium stearate, alkali earth metalstearate calcium, zinc, lauryl sulfate, hydrogenated vegetable oil,sodium benzoate, sodium stearyl fumarate, glyceryl monostearate andpolyethylene glycol 4000.

The scope of the present invention is not limited to using theexcipient, and the excipient can be contained in a usual content rangeby a person skilled in the art.

As described above, the metformin acetate can be applied as variousforms of a preparation for oral administration, and a dosage of thepharmaceutical composition according to the present invention to a humanbody can vary depending on a patient's age, gender, body weight,nationality, health state and disease state and divisionaladministration is also possible pursuant to discretion of a physician.

The present invention will be described in greater detail with referenceto the following examples. The following examples are for illustrativepurposes only and are not intended to limit the scope of the invention.

EXAMPLE 1 Preparation of Metformin Acetate

2 kg (1 equivalent) of metformin hydrochloride and 483 g (1 equivalent)of sodium hydroxide were stirred in 10 L of methanol for 2 hours at roomtemperature, and then remaining solid was filtered and the filtrate wasconcentrated under reduced pressure. Then 15 L of acetone was added tothe resulting solid and stirred. Insoluble material was filtered, andthe filtrate was concentrated under reduced pressure to obtain 1,230 gof metformin free base. The metformin free base was dissolved in 33 L ofacetone, 2.8 L (4 equivalents) of acetic acid was added, and then themixture was stirred for 2 hours at room temperature. The resultingcrystal was filtered, and re-crystallized in water and acetone to obtain1,089 g of metformin acetate (yield: 47.7%).

EXAMPLE 2 Preparation of Metformin Acetate

5 L of water, 2 kg (1 equivalent) of metformin hydrochloride and 578 g(1.2 equivalents) of sodium hydroxide were added to 10 L reactor, andstirred for 2 hours at room temperature. Then 1 L (1.45 equivalents) ofacetic acid was added for 1 hour, and the mixture was stirred overnightat room temperature. The resulting crystal was washed with acetone-water(12:1) mixture, and then acetone, and dried at 60° C. to obtain 1,112 gof metformin acetate (yield: 48.7%).

EXAMPLE 3 Preparation of Metformin Acetate

1 Kg (1 equivalent) of metformin hydrochloride and 2 L of water, andthen 0.5 L (1.45 equivalents) of acetic acid were added to a reactor,and stirred for 2 hours at 30° C. to dissolve thoroughly. Then 289.8 g(1.2 equivalents) of aqueous solution of sodium hydroxide were added tothe reaction solution for 1 hour. The resulting crystal was filtered andwashed with acetone, and then dried at 60° C. to obtain 601 g ofmetformin acetate (yield: 52.7%).

EXAMPLE 4 Preparation of Metformin Acetate

20.0 g (1 equivalent) of metformin hydrochloride and 30 Ml of water, andthen 10 Ml (1.45 equivalents) of acetic acid were added to a reactor,and stirred for 2 hours at 30° C. to dissolve thoroughly. Then 1.23 g(1.5 equivalents) of aqueous solution of sodium hydroxide was added tothe reaction solution. The resulting crystal was filtered and washedwith acetone, and then dried at 60° C. to obtain 16.7 g of metforminacetate (yield: 73.0%).

EXAMPLE 5 Preparation of Metformin Acetate

20.0 g (1 equivalent) of metformin hydrochloride, 50 Ml of water, and19.72 g (1.2 equivalents) of sodium acetate trihydrate were added to areactor, and stirred. Then the resulting crystal was filtered and washedwith acetone, and then dried at 60° C. to obtain 11.72 g of metforminacetate (yield: 51.3%).

EXAMPLE 6 Preparation of Metformin Acetate

0.4 L of water, 241.50 g of sodium hydroxide, 9 L of acetone and 1 Kg ofmetformin hydrochloride were added to a 20 L reactor, and stirred for 2hours and 40 minutes at room temperature. The resulting crystal wasfiltered and washed with acetone. 0.2 L of water and 1 L of acetic acidwere added and stirred. The resulting crystal was filtered and washedwith acetone, and then dried at 60° C. to obtain 1,056 g of metforminacetate (yield: 92.4%).

EXAMPLE 7 Preparation of Metformin Acetate

78 g (1 equivalent) of metformin free base, 234 Ml of isopropanol, 234Ml of water and 57 Ml (1.65 equivalents) of acetic acid were added to areactor, and stirred. The resulting crystal was filtered and washed withisopropanol, and then dried at 60° C. to obtain 54.6 g of metforminacetate (yield: 47.8%).

EXAMPLE 8 Preparation of Metformin Acetate

20.00 g (1 equivalent) of metformin hydrochloride and 4.84 g (1equivalent) of sodium hydroxide were stirred in 200 Ml of ethanol for 2hours at room temperature, and then remaining solid was filtered and thefiltrate was concentrated under reduced pressure. Then 300 Ml of acetonewas added to the resulting solid and stirred. Insoluble material wasfiltered, and the filtrate was concentrated under reduced pressure toobtain 12.0 g of metformin free base. 500 Ml of acetone and 10 Ml (1.45equivalents) of glacial acetic acid were added to the metformin freebase, and then the mixture was stirred. The resulting crystal wasfiltered and washed with acetone, and then dried at 60° C. to obtain13.6 g of metformin acetate (yield: 59.5%).

EXAMPLE 9 Preparation of Metformin Acetate

20.0 g (1 equivalent) of metformin hydrochloride and 50 Ml of water, andthen 10 Ml (1.45 equivalents) of glacial acetic acid were added to areactor, and stirred for 2 hours at 30° C. to dissolve thoroughly. Then10.2 g (1.5 equivalents) of aqueous solution of potassium hydroxide wereadded to the reaction solution. The resulting crystal was filtered andwashed with acetone, and then dried at 60° C. to obtain 13.3 g ofmetformin acetate (yield: 58.2%).

EXAMPLE 10 Pharmaceutical Composition of Metformin Acetate

Metformin acetate, hydroxypropyl methyl cellulose and light anhydroussilicic acid were poured with the content as indicated in Table 2 belowand mixed, and then roller compacted under a pressure of 16 to 17 MPa togive slug. The resulting slug was granulated with No. 14 size, magnesiumstearate was mixed, and the mixture was compressed to prepare a tabletlayer. Then a film-coated layer was formed with Opadry OY-C-7000A as acoating agent using Hi-Coater (SFC-30N, Sejong Machine Co., Ltd, Korea)to prepare a metformin controlled release tablet containing 500 mg ofmetformin acetate.

EXAMPLE 11 Pharmaceutical Composition of Metformin Acetate

Metformin acetate, carboxymethyl cellulose sodium, microcrystallinecellulose and light anhydrous silicic acid were poured with the contentas indicated in Table 2 below and mixed, and then roller compacted undera pressure of 16 to 17 Mpa to give slug. The resulting slug wasgranulated with No. 14 size, magnesium stearate was mixed, and themixture was compressed to prepare a tablet. Then a film-coated tabletwas formed with Opadry OY-C-7000A as a coating agent using Hi-Coater(SFC-30N, Sejong Machine Co., Ltd, Korea) to prepare a metformincontrolled release tablet containing 500 mg of metformin acetate.

EXAMPLE 12 Pharmaceutical Composition of Metformin Acetate

Metformin acetate, polyvinyl pyrrolidone, hydroxypropyl methyl celluloseand glyceryl behenate were poured with the content as indicated in Table2 below with No. 20 size and mixed. Light anhydrous silicic acid wasscreened with No. 35 size, magnesium stearate was mixed, and the mixturewas compressed to prepare a tablet layer. Then a film-coated layer wasformed with Opadry OY-C-7000A as a coating agent using Hi-Coater(SFC-30N, Sejong Machine Co., Ltd, Korea) to prepare a metformincontrolled release tablet containing 750 mg of metformin acetate.

COMPARATIVE EXAMPLE 1 Preparation of Metformin Hydrochloride

500 mg of metformin free base was dissolved in 30 Ml of acetone, andthen 280 Ml of concentrated hydrochloric acid was added, and stirred for2 hours at room temperature. The resulting crystal was filtered andwashed with acetone, and then dried with heated air at 70° C. to obtain490 mg of metformin hydrochloride (yield: 76.4%).

COMPARATIVE EXAMPLE 2 Pharmaceutical Composition of MetforminHydrochloride

Metformin hydrochloride, hydroxypropyl methyl cellulose and lightanhydrous silicic acid were poured with the content as indicated inTable 2 below and mixed, and then roller compacted under a pressure of16 to 17 MPa to give slug. The slug was granulated with No. 14 Size,magnesium stearate was mixed, and the mixture was compressed to preparea tablet. Then a film-coated tablet was formed with Opadry OY-C-7000A asa coating agent using Hi-Coater (SFC-30N, Sejong Machine Co., Ltd,Korea) to prepare a metformin controlled release tablet containing 500mg of metformin hydrochloride.

COMPARATIVE EXAMPLE 3 Pharmaceutical Composition of MetforminHydrochloride

Metformin hydrochloride, carboxymethyl cellulose sodium,microcrystalline cellulose and light anhydrous silicic acid were pouredwith the content as indicated in Table 2 below and mixed, and thenroller compacted under a pressure of 16 to 17 MPa to give slug. The slugwas granulated with No. 14 Size, magnesium stearate was mixed, and themixture was compressed to prepare a tablet. Then a film-coated tabletwas formed with Opadry OY-C-7000A as a coating agent using Hi-Coater(SFC-30N, Sejong Machine Co., Ltd, Korea) to prepare 500 mg of ametformin controlled release tablet containing 500 mg of metforminhydrochloride.

COMPARATIVE EXAMPLE 4 Pharmaceutical Composition of MetforminHydrochloride

Metformin hydrochloride, polyvinyl pyrrolidone, hydroxypropyl methylcellulose and glyceryl behenate were poured with the content asindicated in Table 2 below with No. 20 size and mixed. Light anhydroussilicic acid was granulated with No. 35 size, magnesium stearate wasmixed, and the mixture was compressed to prepare a tablet layer. Then afilm-coated layer was formed with Opadry OY-C-7000A as a coating agentusing Hi-Coater (SFC-30N, Sejong Machine Co., Ltd, Korea) to prepare ametformin controlled release tablet containing 750 mg of metforminhydrochloride.

TABLE 2 Component ratio (mg/tablet) Example Comparative exampleIngredient 10 11 12 2 3 4 Main Metformin 500 500 750 ingre- acetatedient Metformin 500 500 750 hydrochloride Excip- Polyvinyl 120 120 ientpyrrolidone Hydroxypropyl 500 240 500 240 methyl cellulose Carboxymethyl450 450 cellulose sodium Avicel PH101 41 41 Glyceryl 30 30 behenateAerosil 200 5 5 7.5 5 5 7.5 Magnesium 5 4 7.5 5 4 7.5 stearate CoatingOpadry OY- 40 40 60 40 40 60 agent C-7000A Total 1050 1040 1215 10501040 1215

EXPERIMENTAL EXAMPLE 1 Qualitative Confirmation for the Structure ofMetformin Acetate

From X-ray diffraction spectrum, nuclear magnetic resonance spectrumdata, infrared spectrum data and melting point for metformin acetate ofthe formula 1 prepared by Example 1, it was confirmed that metforminacetate according to the present invention has different crystal formand structure from metformin hydrochloride of the formula 4 prepared byComparative example 1.

1) Powder X-ray Diffraction Analysis Spectrum

The characteristic peak for metformin acetate shown in powder X-raydiffraction analysis spectrum depicted in FIG. 1 is indicated in Table 3below. Here “20” means a diffraction angle, “d” means the distancebetween crystal faces, “I/Io” means the relative strength of a peak. Thefollowing analysis was performed by D/MAX-2200V X-ray Diffractometer(XRD) available at Rigaku Company. From comparison of metformin acetateshown in FIG. 1 with metformin hydrochloride shown in FIG. 2, it wasconfirmed that a different crystal was obtained.

TABLE 3 2θ d I/Io 11.940 7.4063 223 15.740 5.6257 318 17.699 5.0070 100019.281 4.5997 618 20.231 4.3666 595 21.399 4.1489 213 21.819 4.0699 15724.040 3.6988 649 26.280 3.3884 501 27.839 3.2020 407 28.540 3.1250 67029.920 2.9839 251 33.480 2.6743 109 35.580 2.5211 102

2) Measurement of Melting Point

It was confirmed that metformin acetate of the formula 1 prepared inExample 1 has a melting point of 227.3˜228.0□, metformin hydrochlorideof Comparative example 1 has a melting point of 222.8˜224.0□.

3) Elemental Analysis

From the elemental analysis for metformin acetate of the formula 1prepared in Example 1, it was confirmed that 1 equivalent of acetic acidis bound in the metformin acetate when comparing actual measurementvalues with the theoretical values of a monovalent salt and a divalentsalt. The analysis results as shown in Table 4 were obtained by FISONSEA-1108 Elemental Analyzer for C, H and N, and Thermo Finnegan FLASHEA-1112 Elemental Analyzer for O.

TABLE 4 Analysis item C (%) H (%) N (%) O (%) Measurement value ofmetformin 38.2 8.2 36.8 17.0 acetate Theoretical value of metformin38.09 7.99 37.01 16.91 monoacetate Theoretical value of metformin 38.557.68 28.10 25.67 diacetate

4) Data for Nuclear Magnetic Resonance Spectrum (NMR)

By confirming the peak of nuclear magnetic resonance (1H-NMR) formetformin acetate of the formula 1 prepared in Example 1 (FIG. 3) andthe peak of metformin hydrochloride of Comparative example 1 (FIG. 4),it could be found that acetic acid is bound to metformin free base sinceit was confirmed that the methyl group of acetic acid was generated inδ=1.885 ppm.

5) Data for Infrared Spectroscopy (FT-IR)

By confirming the peak of infrared spectroscopy (FT-IR) for metforminacetate of the formula 1 prepared in Example 1 (FIG. 5) and the peak ofmetformin hydrochloride of Comparative example 1 (FIG. 6), it could befound that acetic acid is bound to metformin free base since peaks weretotally changed, and in particular, the carbonyl group of acetic acidwas generated at 1622 cm-1.

EXPERIMENTAL EXAMPLE 2 Measurement of Solubility in Water

The solubility of the Metformin acetate of the formula 1 prepared inExample 1 in water were compared with that of the metforminhydrochloride employed as an active ingredient of metforminpharmaceutical composition.

The condition and method of experiment is as follows.

1) Water was filled in an agitated water bath, and its temperature wasset as 30□.

2) 20 mL of water was filled in 100 mL Erlenmeyer flask, and 10 g ofmetformin hydrochloride and metformin hydrochloride were poured thereto,respectively.

3) The Erlenmeyer flasks containing the metformin acetate and themetformin hydrochloride, respectively, were fixed to the rack of thewater bath, and then the apparatus was operated with a speed of 60 timesper minute at 30□.

4) Samples were taken and filtered with an interval of 24 hours, andthen their concentration was calculated by quantitative analysis with anultraviolet spectrophotometer (λ=233 nm).

The above experimental procedures were repeated for 5 days, and thesaturation solubility at 30□ and the velocity reaching the saturationsolubility were obtained and indicated in Table 5 below.

TABLE 5 Saturation Concentration according to the time in solubilityShaking Water Bath (30□) (mg/ml) (mg/ml) 1 day 2 days 3 days 5 daysMetformin 440 347.66 400.25 412.36 534.61 hydrochloride Metforminacetate 280 148.51 233.76 261.66 292.48

As shown in the Table 5, from measurement of each saturation solubilityof the metformin acetate and the metformin hydrochloride after 5 days,it can be seen that the saturation solubilites are 292.48 mg/mL, and534.61 mg/mL, respectively, indicating that the solubility of theacetate is lower than that of the hydrochloride. As shown in the Table5, the metformin acetate has lower saturation solubility than that ofthe metformin hydrochloride, as well as has the speed reaching thesaturation solubility slower than that of the hydrochloride. Therefore,the metformin acetate is advantageous in formulating since desiredrelease rate can be achieved by using less polymeric excipient inpreparing a controlled release tablet of metformin.

EXPERIMENTAL EXAMPLE 3 Measurement of Hygroscopicity

The hygroscopicities of the metformin acetate of the formula 1 preparedin Example 1 and commercially available metformin hydrochloride employedas an active ingredient of metformin pharmaceutical composition werecompared.

The experimental condition and method are as follows.

-   -   1) Metformin hydrochloride and metformin acetate were dried at        40□ for 24 hours, respectively, to reach constant amounts.    -   2) Saturated solution of KH₂PO₄ (22 g/100 g) was filled in the        bottom of a desiccator, and the inner humidity was set to 95%        and the temperature of the desiccator located room was        maintained as 25° C.    -   3) 100 mg of metformin hydrochloride and metformin acetate were        precisely taken, respectively and their weights were measured        together with a container.    -   4) Metformin hydrochloride and metformin acetate were filled in        the desiccator together with the container, and picked up        together in the interval of 24 hours with the container, and        their weights were measured and it was calculated that moisture        was absorbed by the increment in weight.

After repeating the above experimental procedure for 6 days, thehygroscopicity at 95% RH, 25° C. was as indicated in Table 6 below.

TABLE 6 Hygroscopicity (%) 1 day 2 days 3 days 6 days 9 days Metformin6.29 11.86 23.3 60.33 68.78 hydrochloride Metformin 0.35 0.93 1.37 11.2123.32 acetate

As indicated in the Table 6, the hygroscopicity of the metformin acetatewas lower than that of the metformin hydrochloride.

The metformin hydrochloride absorbs moisture during transport and itsparticles are compressed each other to form aggregates due to its highhygroscopicity, but the metformin acetate can decrease greatly thepossibility of changing its status during transport, and can showexcellent fluidity without forming aggregates in pharmaceuticalpreparation steps such as compression step for long period for preparinga product.

EXPERIMENTAL EXAMPLE 4 Confirmation Test of pKa (SpectrographicAnalysis)

The ionized metformin acetate of the formula 1 prepared in Example 1acts as an acid, a free base or an amphipathic compound depending on pH,thereby generating the pH change at each titration point. Thus, pKavalue was obtained from the difference between the calculated pH valueand actually measured pH value. The pKa value is indicated in Table 7below, and its result was depicted in FIG. 9.

TABLE 7 pKa Error Metformin acetate 2.853 ±0.010

EXPERIMENTAL 5 Comparative Dissolution Profile Test Between MetforminAcetate and Metformin Hydrochloride

Dissolution property by paddle method in dissolution test among generaltests in the Korean Pharmacopoeia was measured by using the controlledrelease tablet of the metformin acetate according to the presentinvention prepared by Example 10 and the controlled release tablet ofthe metformin hydrochloride prepared by Comparative example 2, and theresults are shown in FIG. 10.

From the experimental results, when comparing the dissolution propertiesof the controlled release tablet of the metformin acetate designed asall the same preparations except that an active ingredient is different,and the controlled release tablet of metformin hydrochloride, it can befound that the metformin acetate shows lower and extended dissolutionrate by the difference in solubility.

EXPERIMENTAL EXAMPLE 6 Comparative Efficacy Test Between MetforminAcetate and Metformin Hydrochloride

1. Effect of Drop in Blood Glucose Level

This test supports the effect of the present invention. In this test,the metformin acetate of Example 1 and commercially available metforminhydrochloride were administered to an experimental animal, and theprocedure described in Table 8 below was performed in order to comparetheir effects.

TABLE 8 Subject Comparative test for the effects of drop in bloodglucose for metformin acetate and metformin hydrochloride PurposeCompare the effects of drop in blood glucose by administering metforminacetate and metformin hydrochloride to diabetes mellitus inducedexperimental animal Test 210 to 230 g of male rats aged 8 weeks subjectTest 1) Select rats that was judged as healthy during acclimatizingmethod period for 5 days. 2) Induce diabetes mellitus in the rats byinjecting alloxan (40 mg/kg) intravenously twice with an interval of 48hours. 3) Select an individual having at least 13.8 mmol/L of glucoseand divide into three groups 6 days after administration of alloxan. 4)Administer a saline group (control group; n = 5), metforminhydrochloride (0.05 mg corresponding amount as metformin activeingredient; n = 5), metformin acetate (0.05 mg corresponding amount asmetformin inductive ingredient; n = 5) peritoneally to each group. Afteradministration, the glucose concentration in blood was confirmed for 10hours. Evaluation [Measurement of glucose concentration] method 1) Afteradministration of a drug, the glucose concentration in blood wasmeasured at 0, 2, 4, 6, 8, 10 hours. 2) Taking blood of tail vein ateach time frame to measure the glucose concentration in blood with ablood glucose level.

The detailed results of the test for drop in blood glucose are indicatedin Table 9 below.

TABLE 9 Glucose concentration in blood, mmol/L Metformin MetforminControl Hours hydrochloride acetate group 0 13.8 13.8 13.8 2 7.8 6.414.4 4 6.4 7.5 14.2 6 8.6 6.8 14.5 8 7.9 5.9 14.8 10 9.4 6.9 14.4

As indicated in the Table 9, the glucose concentration 10 hours afteradministration of control group was 14.4 mmol/L. The glucoseconcentration 10 hours after administration of metformin acetateadministered group was 6.9 mmol/L, indicating the decrease of about 7.5mmol/L. Meanwhile, the blood glucose concentration in blood 10 hoursafter administration of metformin hydrochloride administered group was9.4 mmol/L, indicating lower glucose concentration in blood than that ofthe control group, but higher glucose concentration in blood than thatof the metformin acetate. In other words, it was confirmed that theeffect of drop in blood glucose of metformin acetate is more excellentthan that of metformin hydrochloride.

2. Test of Drop in Blood Glucose after Meal

This test supports the effect of the present invention. In this test,the metformin acetate of Example 1 and commercially available metforminhydrochloride were administered to an experimental animal, and theprocedure described in Table 10 below was performed in order to comparetheir effects.

TABLE 10 OGTT (Oral Glucose Toerance Test) of metformin acetate andmetformin hydrochloride Subject OGTT of metformin acetate and metforminhydrochloride Purpose Compare the effects of drop in blood glucose aftermeal for metformin acetate and metformin hydrochloride Test subject26~28 g of male ICR mice aged 5 weeks Test method 1) Select mice thatwas judged as healthy during acclimatizing period. 2) Fast the mice for12 hours before test, and then divide into eight groups. 3) Test groupswere set as follows. Animal Administration Test group (number) path G1:No treating control group 8 Oral G2: 100 mg/kg of metformin acetate G3:200 mg/kg of metformin acetate G4: 400 mg/kg of metformin acetate G5:100 mg/kg of metformin hydrochloride G6: 200 mg/kg of metforminhydrochloride G7: 400 mg/kg of metformin hydrochloride G8: Excipientcontrol group 4) 2 g/kg of sucrose was administered orally to G2 to G8 1hour after administering test material to each group. 5) The glucoseconcentration in blood was confirmed for 4 hours after administration ofsucrose. Evaluation [Measurement of glucose concentration] method 1)After administration of sucrose, the glucose concentration in blood wasmeasured at 20, 40, 60, 90, 120, 240 minutes. 2) Taking blood of tailvein at each time frame to measure the glucose concentration in bloodwith a blood glucose level.

The detailed results of the test for drop in blood glucose after mealare indicated in Table 11 below.

TABLE 11 <Unit: mg/dl> Group 0 min 20 min 40 min 60 min 90 min 120 min240 min G1 113.00 ± 2.64 105.25 ± 4.16**  115.13 ± 4.08*  122.75 ±4.88** 113.38 ± 5.85 114.88 ± 5.59 77.00 ± 3.55 G2 101.63 ± 4.94 262.13± 15.33** 212.00 ± 15.68 170.75 ± 17.38  134.50 ± 15.64  106.63 ± 10.4463.63 ± 4.94 G3 101.63 ± 4.58 213.13 ± 11.36** 201.00 ± 21.78 165.75 ±15.91 129.63 ± 8.08 106.38 ± 4.07 80.00 ± 3.73 G4 104.13 ± 6.53 190.25 ±16.05** 169.63 ± 21.19  141.50 ± 18.24*  106.38 ± 13.75   86.25 ±11.25** 69.25 ± 7.96 G5 104.00 ± 6.53 246.00 ± 16.70** 194.38 ± 8.02 151.50 ± 5.45* 122.38 ± 4.69 111.75 ± 6.45 83.63 ± 3.49 G6 107.13 ± 2.84227.50 ± 20.57** 187.25 ± 15.16 147.25 ± 9.89* 121.25 ± 8.15 106.75 ±5.65 87.13 ± 4.50 G7 104.75 ± 3.98 187.38 ± 10.32** 167.63 ± 7.04  135.63 ± 5.53** 110.50 ± 4.78   87.88 ± 9.90** 64.38 ± 7.69 G8 106.13 ±4.06 337.88 ± 24.06  260.00 ± 26.29 198.75 ± 22.16  156.38 ± 18.83 131.00 ± 17.11 81.00 ± 6.48 *Remarkably different with G8, P < 0.05**Remarkably different with G8, P < 0.01

1) The effect of drop in blood glucose could be observed in G3, G4, G6and G7 compared to G8 at 20 minutes after administration of sucrose.

2) The effect of drop in blood glucose could be observed in G3 at 120minutes, and in G2 and G3 at 240 minutes.

3) It could be found that the metformin acetate showed higher effect ofdrop in blood glucose than that of the metformin hydrochloride in 200and 400 mg/kg dosage group at 20 to 60 minutes after administration ofsucrose.

4) From the results, it could be inferred that the effect of drop inblood glucose after meal of the metformin acetate was more excellentthan that of the metformin hydrochloride.

Industrial Applicability

As described above, metformin acetate according to the present inventionis excellent in the effect of drop in blood glucose compared to theprevious metformin hydrochloride, and in particular, is remarkablyexcellent in the effect of drop in blood glucose after meal compared tothe metformin hydrochloride having weak ability of controlling bloodglucose after meal. Further, the present invention enhanced industrialapplicability so that a novel salt of the metformin can be synthesizedwith less cost by improving the steps simply so that the synthesis canbe performed in general production equipment without special equipmentcompared to the previous preparation method that was difficult toperform or must be performed under severe condition. Further, sincemetformin acetate has lower solubility than that of the metforminhydrochloride, excessive drop in blood glucose and quick loss of a drugdue to drastic release can be prevented. Therefore, the metforminacetate is very useful as an active ingredient of a pharmaceutical sinceit is formulated in immediate release form or controlled release formfor 24 hours a day, and thus it is easy to maintain equal concentrationin blood.

The invention claimed is:
 1. A method of treating or preventing obesity,which comprises administrating to a patient an effective amount of apharmaceutical composition containing a metformin acetate of formula 1as an active ingredient


2. The method of claim 1, wherein the metformin acetate is orallyadministrated in amount of 50 to 3,000 mg per a day.
 3. The method ofclaim 1, wherein the metformin acetate is anhydrous metformin acetate.